Method and device for producing hyperpure gallium



Feb. 23, 1965 LEIBENZEDER METHOD AND DEVICE FOR PRODUCING HYPERPURE GALLIUM Filed Sept. 28. 1961 United States Patent 7 4 Claims. dram-s9 My invention relates to a method and apparatus for the production of hyperpure gallium, such as required for the production of electronic semiconductors from gallium compounds, for example, GaP, GaAs, GaSb, or as required for use as doping or contact substance for semiconductor bodies. Hyperpure gallium is also used, for example, in high-temperature thermometers and as a metallic heat-exchange liquid in cooling systems.

Various methods have become known for extreme purification of gallium. Past investigations have mainly been directed to refinement of gallium by electrolytic processes. Among the known refining methods are the precipitation from aqueous medium, as well as the molten-bath electrolysis. The first-mentioned method has only a slight purifying effect, in contrast to molten-bath electrolysis which afford-a high purity of the separated gallium, this purity being dependent to a great extent upon accurate control of electric potentials.

It is an object of my invention to devise a method and apparatus for the production of hyperpure gallium on electrolytic principles in which the refining action is independent, Within a wide range, of accurately constant potentials and, under otherwise comparable conditions, permits a considerable increase in yield by operation at increased electrolytic cell voltages.

To achieve these objects and in accordance with my invention, I employ as electrolyte for electrolytic precipi tation, the solution of a gallium complex of the type Ga(GaX in a non-aqueous organicsolvent, wherein X denotes a halogen element, which as used herein is understood to be chlorine, bromine and iodine. Particularly suitable as the non-aqueous organic solvent are benzene, toluene and xylene, and as gallium complexes are Ga(GaCl Ga(GaBr.,) and Ga(GaI The purifying effect obtained by virtue of the invention is not mainly predicated upon a refining action as known from the electrolysis of aqueous solutions or molten salt, but is rather predominantly based upon the insolubility of many metal halides in the organic solvents to be employed. This results in a considerable advantage over the just-mentioned known methods, namely the fact that the puir-fying action does not depend upon the separation potential so'that relatively high cell voltages can be used trolyte results in the precipitationof gallium. This Was all the less expectablea's the above-mentioned complexes have a salt-like structure. In fact, however, it has been found'that, for example, a solubility of Ga(GaCl and Ga(GaBr in benzene at 20 C. is approximately 1200 g./liter, and is only slightly less than. the solubility in toluene and xylene. The specific electric conductivities (S in ohm" cmr of the electrolytes used according to the invention is indicated in the following Table 1.

3,170,856 Patented Feb. 23, 1965 Table 1 Concentratlon in per- S at S at cent by 22 C. 40 0. weight 52. 4 0.05 0. 07 Gawaoh) i 57. 32

Another advantage over the methods heretofore known resides in the production of the electrolyte. The preparation of the gallium complex to be employed according to the invention is efiected' in known manner through the reduction of GaX (wherein X denotes a halogen element) with gallium in accordance with the following reaction equations:

An example of the technique is given by the production of gallium bromide complex. Commercially available gallium metal is heated in a flow of nitrogen laden with Table 2 Concentration of the foreign elements of the anodic Ga in p.p.m. (10- (percent) the foreign elements of the oath odicallyprecipitated Gain p.p.m. (10- percent) Element Not detectable.

By a second refining operation, the purifying effect can Because of the insolubility of many metal- 7 Concentration of Table 3 Concentration'of the foreign elements of Element the'twice cathodically precipitated Ga in p.p.m. (IO-t Percent) Pb- Not detectable. Fe. ,Do.

A2 D0. Ha D0. Cu -Dc. Si Do. Zn Do. Me 0.0s,

As is further aparent fro m the apparatus described hereinafter, the above-mentioned extreme purity of the refined product is obtained withthe minimum in equipmentand with a good yield per unit of time.

When perform-ingthe methodaccording to my inven-' tion, it is significant that no gas development occurs during the electrolysis so that the process can be carried in a completely closed vessel. This excludes the danger of contamination from the ambient atmosphere. In the electrolytic cells, the contamination can also be avoided to a great extent because the electrolysis can be performed at a temperature of about 50 C., and the electrolyte is only slightly aggressive. To further describe the invention, reference is made to the drawing and the specific example hereinbelow.

The drawing shows a schematic and sectional view of an electrolysis device for performing the above-described method. The anode is formed by molten gallium located at 1 on the bottom of the electrolytic cell. Current is supplied to the anode by a platinum wire 2 which is immersed at its lower end into the molten gallium. The cathode is denoted by 3 and a collector funnel by 4. The funnel 4 is connected with a receiving vessel 5 through a capillary 6. The electrolyte 7 covers the anode 1 and forms part of a thermosiphon system which serves to maintain the electrolyte in circulation. This system comprises the two legs 8 and 9 which are interconnected by transverse portion 13. Leg 9 is surrounded by a cooler 19. Leg 8 has its lower end widened to form an inverted funnel portion at 11 above the cathode 3 and in upwardly spaced relation to the funnel 4. Connected to the circulation system of the electrolyte is a reflux condenser 712. The suction nipple of the reflux condenser 12 is denoted by 14. To prevent contamination, the nipple 14 is closed by a protective cover 15 during operation of the device. A stopcock is provided at 16. The cell vessel is further provided at 17 with a conical ground nipple through which the anode current-supply lead enters into the vessel. The nipple 17 also serves to supply the vessel with electrolyte. purified gallium 19 is sealed by a stoppered ground nippie 18. Conically ground junctions at 21 connect the lower portion of the electrolytic cell with the upper portion that contains the above-described entire electrolytecirculating system.

The quantity of cathode gallium required for starting the process is supplied through the receiving vessel 5 so that the capillary 6 and the receiving funnel 4 are filled with gallium. The anode gallium l is supplied through the central nipple 17 in a quantity suficient to bring the level of the anode gallium to a height of at most a few millimeters below the lower end of the tube 9. Thereafter, the electrolyte is filled into the vessel through the same nipple 17. Since the electrolyte must not be subjected to moisture, the filling must be done in a sealed container through a siphon or pump with the aid of a dry inert gas, for example, nitrogen. The electrolyte, for example, is composed of 50% by weight of Ga(GaBr and 50% benzene.

With nipple 17 open, the electrolyte is inducted through V the suction nipple 14 up to the stopcock 16. Thereafter, the stopcock 16 is closed, the suction line removed from nipple 14, and the protective cap 15 placed over nipple 14. Simultaneously, the condensers and 12 are put into operation, the anode current supply lead 2 is inserted, thus closing the opening of the nipple i7, and the cathode 3 is inserted through nipple 20. A voltage of from about to about v. is applied to the cell between cathode and anode. This results in the flow of an average current value of about 0.4 amp. Precipitation of about 1 g./hour of hyper-pure gallium takes place with a current yield of about 100%. I

Aside from the addition of the anode gallium and the removal of the cathodically precipitated gallium, the device operates practically automatically, continuously and free of maintenance over a long period of time. After starting the process, .the platinum wire of the cathode The receiving vessel 5 for the involves the thermosiphon principle.

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becomes coated with gallium melt, until a drop of gallium is formed at the lower end and drips into the collecting funnel 4. This is repeated continually.

The precipitation is preferably carried out with a high cathode current density which preferably should not be below 200 amperes/decimeter This is aided by the fact that the cathode surface is very small in comparison with the anode surface.

However, if the cathode current density is considerably lowered below the above-mentioned amount, then, according to another embodiment of the invention, the gallium becomes precipitated as a fine pulverulent metal. This powder is suitable, for example, for the production of gallium containing semiconducting sinter materials, which have been recently employed for thermoelectric purposes.

The performance of the electrolyte circulation system That is, the electrolyte heated by the heating bath rises in the leg 8 and passes through the cooled leg 9 back to the lower portion of the electrolytic cell. This affords a relatively simple design despite the required complete sealing of the electrolytic cell. By mounting the cathode at the input funnel 11 of the circulation leg 8, a considerable quantity of loules heat which occurs in the vicinity of the cathode in the electrolyte is advantageously used to amplify the thermosiphon effect.

The circulatory system prevents the occurrence of a solid bottom body of Ga(GaX on top of the anode gallium. Such a body would considerably increase the ohmic resistance of the cell and, for the same cell voltage, would result in a reduction of the current density.

I claim:

1. The method of producing hyperpure gallium for electronic purposes by electrolytic precipitation, which comprises using a solution of a gallium complex of the type Ga(GaX wherein X is a halogen, in a non-aqueous organic solvent.

2. The method of producing hyperpure gallium for electronic purposes by electrolytic precipitation, which comprises using a solution of a gallium complex of the type Ga(GaXr) wherein X is a halogen, in a non-aqueous aromatic organic solvent selected from the group consisting of benzene, toluene and xylene.

3. The method of producing hyperpure gallium for electronic purposes by electrolytic precipitation, which comprises using a solution of a gallium complex of the type Ga(GaX wherein X is a halogen, in a non-aqueous aromatic organic solvent selected from the group consisting of: benzene, toluene and xylene, and adjusting the current density above 200 amperes/square decimeter to precipitate gallium at the cathode in liquid form.

4. The method of producing hyperpure gallium for electronic purposes by electrolytic precipitation, which comprises using a solution of a gallium complex of the type Ga(GaBr in a non-aqueous aromatic organic solvent selected from the group consisting of benzene, toluene and xylene, and adjusting the current density below 200 amperes/square decimeter to precipitate gallium at the cathode in pulverulent form.

References Cited in the file of'this patent UNITED STATES PATENTS 2,440,238 Alley et a1 Apr. 27, 1948 2,928,731 Gebauhr Mar. 15, 1960 2,952,589 Ziegler et al Sept. 30, 1960 2,985,568 Ziegler et al May 23, 1961 2,998,374 Crantors Aug. 29, 1961 3,007,858 Braithwaite Nov, 7, 1961 FOREIGN PATENTS 126,270 I Russia June .4, 1959 

3. THE METHOD OF PRODUCING HYPERPURE GALLIUM FOR ELECTRONIC PURPOSES BY ELECTROLYTIC PRECIPITATION, WHICH COMPRISES USING A SOLUTION OF A GALLIUM COMPLEX OF THE TYPE GA(GAX4) WHEREIN X IS A HALOGEN, IN A NON-AQUEOUS AROMATIC ORGANIC SOLVENT SELECTED FROM THE GROUP CONSISTING OF BENZENE, TOLUENE AND XYLENE, AND ADJUSTING THE 